The present invention relates generally to molded impellers, and more particularly to a molded impeller having a locating insert therein.
Prior art pump impeller assemblies include an over-molded knurled insert for retaining and locating the impeller on a driveshaft. The insert includes internal threads that mate with external threads on the driveshaft and serve to locate the impeller relative to the driveshaft. It is important that the insert be properly positioned on the shaft because it locates the impeller, and such positioning, if incorrect, may reduce seal life, increase vibration and cause fluid leakage. However, prior art inserts, and the threads therein, do not satisfactorily locate the impeller on the driveshaft. This may be due in part to the difficulty of exactly controlling the location of thread surfaces. Moreover, the threads may not satisfactorily locate the impeller during molding of the impeller. The latter problem can cause eccentricity or “wobble” of the impeller during operation, necessitating a secondary machining operation or other measure to prevent contact of the impeller inlet with the pump housing. Such added manufacturing operations add to the cost of the impeller. In some cases a secondary seal ring must be added between the impeller and the housing, which again adds cost. Accordingly, an improved insert for the impeller is needed.